It is known that trichlorophenols may provoke free radical formation, leading to oxidative stress in living organisms, but no effort has been undertaken to evaluate oxidative changes in plants exposed to 2,4,5- trichlorophenol (2,4,5-TCP) that commonly exists in a soil environment. In this work the effect of 2,4,5-TCP on selected parameters of an antioxidative system, the content of hydrogen peroxide and the activity of glutathione S-transferase in the leaves of reed canary grass (Phalaris arudinacea), has been investigated. An increase in the content of total and reduced forms of glutathione and ascorbate, as well as free phenols concentrations, was shown. Moreover, a rise in the activities of catalase, guaiacol peroxidase, and glutathione S-transferase along with arisen content of hydrogen peroxide was observed. The obtained results showed that oxidative stress was provoked in the examined plants that had been exposed to 2,4,5-trichlorophenol.